1. Field of the Invention
The invention relates to an optical disc drive, more particularly to an optical disc drive with a system behavior detection module.
2. Description of the Related Art
As illustrated in FIGS. 1 and 2, a conventional optical disc drive comprises a servo system that includes an optical pickup unit 11, an amplifier (or pre-amplifier) 12 coupled to the optical pickup unit 11, a compensator 13 coupled to the amplifier 12, and a driver unit 14 coupled to the optical pickup unit 11 and the compensator 13.
The conventional optical disc drive further includes a controller chip (not shown). The amplifier 12 and the compensator 13 are normally built into the controller chip.
In operation, the optical pickup unit 11 emits light that is reflected by an optical disc (not shown). The reflected light is detected by the optical pickup unit 11, which responds by providing a detected signal (DS) corresponding to the reflected light. The amplifier 12 receives the detected signal (DS) and provides an error signal (ES), such as a track error or focus error signal, corresponding to the detected signal (DS). The compensator 13 receives the error signal (ES) and a reference signal (RS), and provides a control signal (CS) corresponding to the error signal (ES) and the reference signal (RS). The driver unit 14 receives the control signal (CS) and drives movement of the optical pickup unit 11, i.e., movement of an object lens (not shown) of the optical pickup unit 11, in accordance to the control signal (CS), thereby resulting in correction of the focusing and tracking of the light emitted by the optical pickup unit 11.
In order for the driver unit 14 to drive movement of the optical pickup unit 11 so that the light emitted by the optical pickup unit 11 can be accurately focused on the tracks on the optical disc, the compensator 13 must be designed based on the behavior of the servo system during the development stage of the optical disc drive.
A conventional method for detecting the behavior of the servo system comprises the following steps of cutting the electrical connection between the compensator 13 and the driver unit 14, connecting an adder circuit 15 between the compensator 13 and the driver unit 14, using a dynamic system analyzer 20 to introduce an exciting signal (XS), such as a variable frequency sinusoidal signal, into the servo system through the adder circuit 15, using the system analyzer 20 to obtain output and input signals from a junction 161 of the compensator 13 and the adder circuit 15, and a junction 162 of the adder circuit 15 and the driver unit 14, and using the system analyzer 20 to calculate gain and phase relationships between the input and output signals. The gain and phase relationships calculated by the system analyzer 20 can then be used as parameters in designing the compensator 13.
Although the above-mentioned method achieves the purpose of detecting the behavior of the servo system, the alteration of the circuitry of the servo system to connect the adder circuit 15 may arise in interference to the exciting signal (XS). As a result, the resulting calculation of the gain and phase relationships may not be accurate. Furthermore, the system analyzer 20 is not economically practical for this purpose due to its high cost.